Human-powered vehicles to the present time have relied upon and made use of a discrete set of power transfer ratios to obtain torque during acceleration and power at high speeds. While this has been effective there has been a long-felt need for a more efficient means of transferring and utilizing the limited power available. The present invention addresses this specific issue through the ability to adjust the speed ratio to meet specific requirements and/or demands at any instant in time. Another advantage of the present invention is the ability to retrofit to the widest range of human-powered vehicle applications due to its light-weight compact design.
While there are several examples of continuously variable transmissions of similar design, such prior art devices as are disclosed in the U.S. Pat. No. 4,270,400, issued to Fodor on Jun. 2, 1981 and 4,137,785, issued to Virlon on Feb. 6, 1979, these mechanisms relate to the automotive industry. Thus, these devices are heavy-duty in nature, bulky in design, and are not appropriate for a human-powered vehicle, for example a bicycle or a wheelchair. Other prior art devices as are disclosed in the U.S. Pat. No. 3,934,481, issued to Foster on Jan. 27, 1976 and 3,863,503, issued to Nelson in October of 1960 are appropriate for a bicycle but are complex in design requiring a number of precision-machined components and would not be applicable to other human-powered vehicles, for example a wheelchair. These prior art devices maintain a sufficient frictional contact pressure through either a constant overload of the contact pressure between each idler and disk face, or use of a complex mechanism to sense and control this contact pressure at any given point in time. Thus, service life is shortened through either high frictional wear or the addition of complex precision-made components.
There are examples of other drive mechanisms, such as U.S. Pat. No. 583,500, issued to Mueller in June 1897, 723,228, issued to Banwell in March 1903, and 4,955,247, issued to Marshall in September 1990. While each of these may be applicable to a human-powered vehicle, none is sufficiently compact or lightweight to be practical in current bicycle or wheelchair designs, each requiring extensive modifications to the supporting flames of the target vehicle. There are other examples of drive mechanisms which might be considered as appropriate for existing frame designs, such as U.S. Pat. No. 536,550, issued to Snyder in March 1895, and 743,133, issued to Bacon in November 1903. These devices are positive in drive nature, suffering the inability to reach a broad range of precision ratios, and offer no clear benefit over currently existing technology.
The present invention provides variable contact pressure between idler and disk, enforcing higher contact pressure at lower speed ratios, when the potential torque demands are at a maximum. Conversely, at higher speed ratios, when the potential is minimized, the contact pressure is lessened. This functionality is achieved through a simplified means requiring a minimum of precision-made components, thereby extending service life.